In industrial production, it is difficult to produce oscillators having a well-defined reference frequency, in order to obtain, at the output of a series of dividers, timing pulses at a reference unit frequency, such as at 1 Hz. Such oscillators are generally arranged to be produced at the end of the production phase with a reference frequency in a slightly higher frequency range. This makes it possible, over base or inhibition periods, for example having a duration of around a minute, to deliberately inhibit one or more clock pulses by means of an inhibition circuit in order to correct on average the reference frequency.
To improve the precision of the time base clock frequency, it may also be envisaged to increase the inhibition period, but the maximum error between two time measurements increases in proportion to the factor of increase of the inhibition period. Increasing the inhibition period to increase precision does not allow for accurate checking of the clock frequency over a short period. The test time cannot be determined simply on the basis of a certain number of successive inhibition periods, which constitutes a drawback.
The Patent Application CH 707 285 A2 describes a method for regulating a quartz oscillator for an electronic watch. To achieve this, it is provided that some pulses are inhibited over a defined period. With the method described, it is possible to increase the precision of the electronic watch movement ensuring that it can be successfully certified by a certification body, such as the COSC (Swiss Official Chronometer Testing Institute) in Switzerland. However, the timepiece circuit is not configured to be capable of changing into an accelerated test mode, which constitutes a drawback.
The Patent Application WO 2014/095538 A2 may be cited, which discloses a thermocompensated chronometer circuit. The electronic watch includes at least one electric motor for driving the time display hands. It also includes a watch module with a time base, which supplies a clock signal connected to a divider chain to supply a reference clock signal for controlling the electric motor. The watch module further includes a measurement and correction circuit between the time base and the dividers, so as to supply a temperature compensation signal to the watch module. There is not, however, described a watch module capable of being configured to be placed in an accelerated test mode for an electronic watch rate test method, which constitutes a drawback.
In order to measure the proper rate of a quartz watch, particularly to determine its time-keeping precision over a long period, the watch must be tested. Generally speaking, this test is performed on measuring equipment by detecting the pulses from the motor, which is clocked to the second, via a magnetic coupling. The duration of an end of production test is long, given that to accurately determine the proper rate of the watch, close to 4 hours of testing are required, which constitutes a drawback of this type of test.
A time base device for a timepiece circuit of an electronic watch includes a watch module having a 32 kHz quartz crystal, which operates in conjunction with an integrated watch circuit. This integrated circuit thus includes an oscillator connected to the quartz, a temperature sensor, a temperature compensation circuit, a circuit for adjustment of the clock frequency by inhibition, and a motor pulse generator. To achieve high precision, the time base device effects an inhibition cycle with a long period. For example, such a circuit can effect inhibition at a frequency of 16 kHz with a resolution of ±1 clock pulse every 960 seconds, i.e. every 16 minutes. This corresponds to 61 μs every 960 seconds or 0.0636 ppm or 2.005 seconds per year.
There are practical difficulties in calibrating and checking the time base device during the manufacturing method. According to the prior art, in order to check the frequency accuracy of the watch, it is necessary to accurately measure the time between motor pulses over a relatively long period, typically around 16 minutes, as indicated above. This long time period requires heavy and expensive equipment, which is produced, for example by Witschi Electronic AG. This equipment is capable of measuring products in batches, for example a batch of 32 pieces, which are measured within the 16 minutes. This equates to a production of 2 pieces per minute, but is still relatively long for performing the test, which constitutes a drawback.